Software Vulnerabilities Detection System and Methods

ABSTRACT

This invention discloses a system and methods of detecting software vulnerabilities in a computer program. The invention models compiled software to examine both control flow and data flow properties of the target program. A comprehensive instruction model is used for each instruction of the compiled code, and is complemented by a control flow graph that includes all potential control flow paths of the instruction. A data flow model is used to record the flow of unsafe data during the execution of the program. The system analyzes the data flow model and creates a security finding corresponding to each instruction that calls an unsafe function on unsafe data. These security findings are aggregated in a security report along with the corresponding debug information, remediation recommendations and any ancillary information related to each instruction that triggered the security finding.

RELATED APPLICATIONS

This invention is a Continuation of now allowed U.S. patent applicationSer. No. 14/460,636 filed on 15 Aug. 2014. The above numberedapplication is incorporated by reference herein in its entirety.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under the CyberFastTrackprogram documented in DARPA PA-11-53 dated Jan. 31, 2013, awarded byDefense Advanced Research Projects Agency (DARPA).

FIELD OF THE INVENTION

This invention relates generally to ensuring software security and inparticular to exposing software vulnerabilities by performing static anddynamic analysis of compiled software.

BACKGROUND ART

Software security and vulnerability checking is an active field ofacademic and industrial pursuit. With the news of exploitation ofsoftware vulnerabilities by hackers a commonplace occurrence, it isunsurprising to see many academic and professional institutions focusingtheir efforts to develop tools and practices that aim to make softwaremore secure against exploitative attacks from global hackers andadversaries.

There are many ways of detecting and addressing vulnerabilities insoftware in the prior art. U.S. Pat. No. 8,499,353 discloses securityassessment and vulnerability testing of software applications based inpart on application metadata in order to determine an appropriateassurance level and associated test plan that includes multiple types ofanalysis. Steps from each test are combined into a “custom” or“application-specific” workflow, and the results of each test thencorrelated with other results to identify potential vulnerabilities.

U.S. Pat. No. 8,365,155 describes a software analysis frameworkutilizing a decompilation method and system for parsing executable code,identifying and recursively modeling data flows, identifying andrecursively modeling control flow and iteratively refining these modelsto provide a complete model at the nanocode level. The nanocodedecompiler may be used to determine flaws, security vulnerabilities, orgeneral quality issues that may exist in the code.

U.S. Pat. No. 8,739,280 describes a context-sensitive taint analysissystem. Taint processing applied to a tainted value of an application isidentified and an output context of the application associated withoutput of the tainted value is determined. It is determined whether thetaint processing is effective in mitigating a security vulnerabilitycaused by the tainted value for the output context.

U.S. Pat. No. 8,347,392 describes an apparatus and method for analyzingand supplementing a program to provide security. A computer readablestorage medium has executable instructions to perform an automatedanalysis of program instructions. The automated analysis includes atleast two analyses selected from an automated analysis of injectionvulnerabilities, an automated analysis of potential repetitive attacks,an automated analysis of sensitive information, and automated analysisof specific HTTP attributes. Protective instructions are inserted intothe program instructions. The protective instructions are utilized todetect and respond to attacks during execution of the programinstructions.

Non-Patent reference, “Dynamic Taint Analysis for Automatic Detection,Analysis” by James Newsome and Dawn Song of Carnegie Mellon University,proposes a dynamic taint analysis solution for automatic detection ofoverwrite attacks. The approach does not need source code or specialcompilation for the monitored program, and hence works on commoditysoftware. To demonstrate this idea, they implemented TaintCheck, amechanism that can perform dynamic taint analysis by performing binaryrewriting at run time.

Non-Patent reference, “gFuzz: An instrumented web application fuzzingenvironment” by Ezequiel D. Gutesman of Core Security Technologies,Argentina, introduces a fuzzing solution for PHP web applications thatimproves the detection accuracy and enriches the information provided invulnerability reports. They use dynamic character-grained taint analysisand grammar-based analysis in order to analyze the anatomy of eachexecuted SQL query and determine which resulted in successful attacks. Avulnerability report is then accompanied by the offending lines ofsource code and the fuzz vector (with attacker-controlled charactersindividualized).

One shortcoming of prior art teachings is that they suffer from pooraccuracy while also at times requiring source code for analysis asopposed to just bytecode/assembly code, or they attempt to simplify thebytecode/assembly code before analysis. Other prior art work teachesrunning both dynamic and static analysis components in an independent orserial fashion. Furthermore earlier approaches attempt to exhaustivelymap all data flows in a decompiled or intermediate representation of asoftware system which impairs performance and slows the overall process.Relatedly, prior art teachings do not provide for advantages afforded byconcurrent multi-core or multi-CPU processing infrastructure that iscommonplace these days, to allow for distributed analysis of very largetarget software systems with high precision.

OBJECTS OF THE INVENTION

In view of the shortcomings of the prior art, it is an object of thepresent invention to provide for high-precision software analysis systemand methods that do not require the source code of the analyzed program.

It is another object of the invention to not require an exhaustiveprocessing of all data flows in a program but rather than the ones thatinclude unsafe data.

It is another object of the invention to not rely on decompliation ofexecutable binary code.

It is yet another object of the invention to allow for distributedprocessing of the analysis framework taught by the invention by takingadvantage of a multi-CPU or multi-core processing environment,consequently allowing for analysis of very large target software systemswith efficiency and high precision.

Still other objects and advantages of the invention will become apparentupon reading the detailed description in conjunction with the drawingfigures.

SUMMARY OF THE INVENTION

The objects and advantages of the invention are secured by a system andmethods of detecting software vulnerabilities in a computer program byanalyzing the compiled code of that computer program. The inventionoptionally uses the source code of the computer program in conjunctionwith the compiled code, but having the source code is not a requirementof the invention. The invention teaches utilizing an instruction modelfor each instruction of the compiled code. The instruction model for agiven instruction includes the instruction location, debug information,instruction type, operands, existing memory state requirements, bytecodemetadata, potential security attributes, basic block membership andfunction/method membership if applicable, of that instruction.

The invention further uses a control flow graph for each instructionthat complements the instruction model of that instruction, and includesall potential control flow paths, and a bidirectional list ofpredecessor instructions of that instruction. Preferably, the compiledcode is instrumented at random and critical points in the code. There isa data flow model to record the flow of unsafe data during the executionof the program. The system has the means to analyze the data flow modeland to create a security finding corresponding to each instruction thatcalls an unsafe function on unsafe data. These security findings areaggregated in a security report along with the corresponding debuginformation and the optional source code information for eachinstruction that triggered the security finding.

In the preferred embodiment of the invention, the instruction model alsoincludes placeholders for additional attributes. These additionalattributes may include information for pointer aliases or unsafe dataflow. The pointer alias information may include an aliasing mapcontaining pointers that have the same address values given a subset ofor all possible control flows of the instructions of the compiled code.

In another embodiment, the instruction model also contains attributesthat are deduced from other attributes of the instruction model. Thesederived attributes may include values for memory locations, processorregisters and variable types associated with the given instruction ofthe instruction model. In another preferred embodiment, the flow ofunsafe data is recorded in a data flow file that utilizes a common fileformat such as XML, based on which the data flow model is at leastpartially populated. In an advantageous embodiment of the invention, ananalyzer module is used to analyze the instruction model, control flowgraph and the data flow model to detect software vulnerabilities in thecompiled code.

In a highly advantageous embodiment of the invention, a set ofconcurrent worker threads are spawned that take advantage of amulti-core or multi-node or multi-machine or multi-CPU processingplatform, to analyze instructions where an unknown or unsafe externalinput (or taint) data is provided to the program and an unsafe functionor method is called upon it. In another preferred embodiment of thesystem, the security findings in the security report also contain a fulltrace of the unsafe data at the instruction that triggered the securityfinding, along with the line numbers of the source file if available, ahuman-readable description of the finding, a risk rating and optionallyone or more recommendations to address the security finding.

The methods of the invention further provide the steps required to carryout the operation of the system. The invention teaches the stepsrequired to detect software vulnerabilities of a computer program bytaking as input the compiled code of the program, and optionally itssource code. It then creates an instruction model and a control flowgraph for each instruction in the compiled code. If further creates adata flow model to record the flow of unsafe data during the executionof the compiled code. The compiled code is instrumented at random andcritical control flow points of the program.

For a given instruction, the instruction model includes the instructionlocation, debug information, instruction type, operands, existing memorystate requirements, bytecode metadata, potential security attributes,basic block membership, function/method membership if applicable, andclass membership of the given instruction. The instruction model alsoincludes placeholders for additional attributes, including pointeraliasing information, unsafe data flow information and attributes thatare deduced from other attributes including values of memory locations,values of processor registers and variable types for the giveninstruction.

For each instruction, the control flow graph is populated with allpotential control flow paths, and a bidirectional list of predecessorinstructions. Finally, for each instruction, the data flow model ispopulated by running the compiled code with the instrumentation at leastonce and recording the flow of unsafe data for each run. In anotherpreferred embodiment, this recording of unsafe data flow is first donein a data flow file in a common file format such as XML, and thepopulation of the data flow model is based on the data flow file.

The compiled code is scanned according to the methods provided by theinvention to find each instruction where an external input is suppliedto the program, denoting unknown, unsafe data. If that instruction callsan unsafe function on the unsafe data, this triggers the creation of asecurity finding. As the analysis is performed, all security findingsare aggregated in a security report.

In the preferred embodiment, each security finding in the securityreport includes the debug information for the instruction that triggeredthe finding, along with the line numbers of the source code ifavailable, a trace of the unsafe data from its origin to termination,identifier values of any processor registers or variables containing theunsafe data, a description of the security finding, a risk rating, andoptionally one or more recommendations to address/remedy the securityfinding. Appropriate highlighting of these elements in the securityreport is also performed to make the report visually presentable,readable and easy to consume.

In another advantageous embodiment, three lists are created for eachinstruction. These lists are Unsafe1, Unsafe2 and Unsafe3. Allinstructions that are determined to be unsafe i.e. they use unsafe databy calling an unsafe function, are added to a list called Worklist. Aset of concurrent worker threads are spawned, each thread selecting andprocessing an instruction at random from Worklist. Based on the controlflow graph and data flow model earlier created, for each instruction inWorklist, Unsafe1 list is populated with incoming unsafe data at thatinstruction, Unsafe2 list with unsafe data currently being processed bythat instruction, and Unsafe3 list with unsafe data that has been fullyprocessed by that instruction.

As the worker threads process the instructions, the contents of thethree lists for each instruction are updated based on the control flowgraph of that instruction as data flows from its Unsafe1 list to Unsafe2list to Unsafe3 list and into the Unsafe1 list of the downstreaminstruction. If new unsafe data is added to the Unsafe1 list of aninstruction that calls an unsafe function, it is re-added to theWorklist and a security finding is generated, and the above process isrepeated. Ultimately, the spawning of worker threads is concluded whenthere are no more unsafe instructions left in Worklist, or apredetermined timeout period has elapsed during the above processing.

Concurrency locks are provided for each of the three lists, Unsafe1,Unsafe2 and Unsafe3 above, and at each step of the above processing,these locks are used to ensure the integrity of the contents of theselists. When a list is no longer being used, its concurrency lock isreleased (unlocked).

In a highly advantageous embodiment, worker threads are distributedacross a multi-core or multi-processor or multi-CPU processingenvironment to improve the performance of the analysis and to allowprocessing of very large target software programs. In a similarlyadvantageous embodiment, the traversal of the control flow graph by theworker threads is performed according to custom unsafe data propagationrules provided by the user. In another advantageous embodiment thesecurity findings are created by an analyzer module.

Clearly, the system and methods of the invention find many advantageousembodiments. The details of the invention, including its preferredembodiments, are presented in the below detailed description withreference to the appended drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a block diagram view of the software vulnerabilities detectionsystem according to the current invention.

FIG. 2 is a conceptual diagram of the instruction model according to thecurrent invention.

FIG. 3 is a diagram of the control flow graph of an instructionaccording to the invention.

FIG. 4 is a conceptual diagram of the data flow model of an instructionaccording to the invention.

FIG. 5 is a detailed block diagram view of the elements and theirworkings according to the current invention.

FIG. 6 is a flowchart comprising the analytical steps of the algorithmrequired for the detection of software vulnerabilities according to thecurrent invention.

DETAILED DESCRIPTION

The figures and the following description relate to preferredembodiments of the present invention by way of illustration only. Itshould be noted that from the following discussion, alternativeembodiments of the structures and methods disclosed herein will bereadily recognized as viable alternatives that may be employed withoutdeparting from the principles of the claimed invention.

Reference will now be made in detail to several embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying figures. It is noted that wherever practicable, similar orlike reference numbers may be used in the figures and may indicatesimilar or like functionality. The figures depict embodiments of thepresent invention for purposes of illustration only. One skilled in theart will readily recognize from the following description thatalternative embodiments of the structures and methods illustrated hereinmay be employed without departing from the principles of the inventiondescribed herein.

The present invention will be best understood by first reviewing thesoftware vulnerabilities detection system 100 according to the currentinvention as illustrated in FIG. 1. Vulnerabilities detection system 100comprises computer program 102 in the form of its compiled code 104 andoptionally source code 106 that resulted in its compiled code 104.Computer program 102 is the target program to be analyzed by system 100for software vulnerabilities. Having source code 106 is desirable butnot required by software vulnerabilities detection system 100 accordingto the invention. Vulnerabilities detected by system 100 in computerprogram 102 may allow exploitative attacks by potential adversaries orhackers. Such attacks include, but are not limited to denial of serviceattacks, code injection attacks and 2nd order attacks such as cross-sitescripting (XSS) attacks.

Software vulnerabilities detection system 100 comprises instructionmodel 110, control flow graph 112 and data flow model 114. Based oninstruction model 110, control flow graph 112 and data flow model 114,software vulnerabilities detection system 100 performs analysis 116 toproduce security report 118 comprising the security findings discoveredduring analysis 116.

Readers with average skill in the art will understand that compiled code104 can be executable binary code, machine code, or object code that canrun directly on a hardware platform such as x86, Sparc, Mac, HP, IBMMainframe, etc. or it can be an intermediate bytecode or portable codethat can run in a given runtime environment such as Java Virtual Machine(JVM). Source code 106 can be in any programing language such as C, C++,Java, Assembly, Cobol, SQL, etc. Furthermore, source code 106 can be inany 2^(nd), 3^(rd), 4^(th) or higher generation programming languagewithout departing from the principles of the invention. A highlyadvantageous feature of the current invention is that source code 106 isdesirable, but not required to achieve the objects of the invention. Notrequiring the presence of source code 106 overcomes many practicallimitations of the prior art.

Instruction model 110 is a programming construct used by the inventionto model each instruction of compiled code 104. This programmingconstruct comprises all the necessary and desirable attributes requiredby system 100 to model each instruction of compiled code 104. Theseattributes include the location (e.g. base address and relative memorylocation of the instruction), debug information if available (e.g.variable name annotations and/or source code line annotations), type ofthe instruction (e.g. mov, add, sub), its operands (e.g. eax register,an integer immediate value, operand stack reference, local valuereference), its potential security attributes.

These attributes further include existing memory state requirements ofthe instruction (e.g. basic block derived invariant conditions), basicblock membership (e.g. start and end references for all basic blocksencompassing an instruction), function/method membership (e.g. whatfunctions/methods the instruction belongs to) and/or class membership(e.g. which object classes the instruction belongs to), if applicable.Those with average skill in the art will find these attributes familiarfrom the fundamentals of software engineering and computer programming.FIG. 2 provides a conceptual representation of instruction model 110using a familiar notation for data structures and member associations incomputer programming.

Referring to FIG. 1, during the execution of compiled code 104, userinput 108 may be provided by the operator or user of computer program102 whose vulnerabilities are to be detected. Those familiar with theart will understand that user input 108 represents a potential securityrisk for computer program 102 as it may intentionally or otherwise,violate the bounds of a program variable which may affect the integrityof computer program 102 or the data it is operating on. Thus user input108 represents ‘taint’ or unsafe data, as will be understood by skilledpeople of the art. User input 108 can be provided in many differentways, for example, via a web form and keyboard, a file, an input/outputbuffer or stream, a pipe, screen redirect, etc.

Compiled code 104 according to the invention is preferably instrumentedat random and critical control flow points of the program. Thosefamiliar with the art will understand that instrumentation may refer tocode instructions and metadata augmented to the computer program thatallow monitoring of its behavior, performance and operation more closelythan during normal execution, and may generate additional logging anddebug output to the screen or files as desired. As provided by theinvention, computer program 102 is preferably instrumented at randompoints within the program. Instead of or in addition to that, theprogram is also preferably instrumented at points where there is acritical control flow transition in the program.

Those familiar with the art will understand that there are many ways todetermine these points where instrumentation may be provided in computerprogram 102. In a preferred embodiment, instructions in compiled code104 can be randomly selected for instrumentation. Alternatively or inaddition, a pre-processor can be used to determine the critical controlflow points in program 102 prior to its execution, and theninstrumentation can be added at those points in program 102. Indeed, itis allowed by the invention to instrument entire or none of computerprogram 102, without departing from the principles of the invention. Theinstrumentation of program 102 allows observing and modification ofunsafe data as it flows through program 102 according to the teachingsof the invention.

The invention further uses control flow graph 112 for each instructionthat complements instruction model 110 of that instruction. Control flowgraph 112 for a given instruction of compiled code 104 is populated withall potential control flow paths of that instruction, assuming there isno overwriting of the underlying instructions. Control flow graph 112for a given instruction also contains a bidirectional list of itspredecessor instructions. FIG. 3 represents control flow graph 112 foran instruction I according to the teachings of the invention. In FIG. 3,each instruction is represented by a circle. Instruction I has 4predecessor instructions P and 3 successor instructions S representingall possible control flow paths for I as shown in the figure. All Pinstructions will be contained in a bidirectional list in control flowgraph 112 for instruction I as represented by the dashed line in FIG. 3.

Referring back to FIG. 1, the invention further comprises data flowmodel 114. During the execution of program 102, the movement of unsafedata is recorded in data flow model 114. The movement of unsafe data, asa result of successive instructions, is recorded in data flow model 114according to the teachings of the invention. FIG. 4 represents anexample data flow model 114 populated according to the teachings of theinvention.

In FIG. 4, variable V1 contains unsafe data that may have beenpreviously supplied by user input 108 as taught earlier (see FIG. 1).Tainted data V1 is then moved to processor register AX in the nextinstruction of one control flow path, and then copied to variable V2.The subsequent instruction then calls an unsafe function on variable V2representing a potential security risk in the computer program. FIG. 4also illustrates additional control flow paths in data flow model 114where the unsafe function call is performed on the tainted datacontained in variable V2. Those familiar with the art will know thevarious types of unsafe function calls that may result in a potentialsecurity flaw in the code that can be exploited by an adversary. Forexample, in C/C++ “char*strcpy(char*dest, const char*src)” function ontainted data is an unsafe function call, because it can allow a securitycondition called buffer overflow to happen and damage the integrity ofcomputer program 102 of FIG. 1, or its data, or worse allow a maliciousadversary to inject harmful code or virus into the computer program.

According to the teachings of the current invention as explained above,data flow model 114 only records the flow of unsafe data during theexecution of the program, as opposed to attempting to include and recordall potential data flows. This significantly reduces the performanceoverhead and memory requirements of software vulnerabilities detectionsystem 100, allowing it to analyze large target software systems morecomprehensively than possible through the teachings of prior art. Thisalso allows the current invention to not require decompilation ofcompiled code, as required by some prior art teachings.

According to the main embodiment of the invention, based on instructionmodel 110, control flow graph 112 and data flow model 114, allinstructions in computer program 102 that call an unsafe function onunsafe data, trigger a security finding which is recorded in securityreport 118 as represented in FIG. 1. Each such security finding containsdebug information of the instruction that triggered the securityfinding, along with its source code information, if available. Securityreport 118 exposes the vulnerabilities in computer program 102 that canbe appropriately remediated to prevent exploitative attacks by amateurand professional adversaries according to the teachings of theinvention.

As represented in FIG. 2, instruction model 110 further includesplaceholders for additional attributes or deduced attributes that maynot be immediately known at the time of the initial creation ofinstruction model 110. These additional attributes may include pointeraliases. Pointer aliases represent pointers that point to or contain thesame memory address for multiple control flow paths of computer program102.

In addition, instruction model 110 for a given instruction I may includeinformation related to its predecessor instructions P as represented inFIG. 3, and any additional information or metadata as deemed necessaryto facilitate recording of the flow of unsafe data as represented inFIG. 4. Furthermore, instruction model 110 may also include informationdeduced from other attributes. Examples of such derived attributesinclude memory locations or addresses, processor registers and variabletype information for the given instruction based on its type, debuginformation and bytecode metadata.

According to an additional embodiment of the invention, analysis 116 inFIG. 1 may be performed by an analyzer module. Analyzer module may be apart of system 100 or may be external to it. If it is external to system100, appropriate remote invocation calls or function calls or remoteprocedure calls (RPC) may be implemented to call the external module, aswill be obvious to those skilled in the art. Indeed it is possible thatthe analyzer module is a 3^(rd) party software with its own applicationprogramming interface (API), without departing from the principles ofthe invention. Similarly, in a highly advantageous embodiment, analysis116 is performed by worker threads that are spawned specifically forthat purpose. These worker threads may then be distributed across acluster of computing nodes, processors or cores, in a multi-CPU ormulti-core, parallel processing environment.

Further embodiments provide security report 118 of FIG. 1 to include anexecution trace of unsafe data corresponding to each security findingpopulated in the report. The execution trace may contain the origin andtermination information for the unsafe data that ultimately caused thesecurity finding to be triggered. For example, if unsafe data wasprovided as a user input in function or instruction I1 and it traversedthrough several intervening functions or instructions I2 . . . I9 beforebeing discarded or reset in instruction I10, then execution trace forthe corresponding security finding in security report 118 may containthe entire lifecycle or trace of that data along with the names offunctions or instructions I1 . . . I10.

In addition, security report 118 may contain a human friendlydescription of the security finding, and a risk rating or risk factorassigned to the security finding by system 100. Depending on theseverity of the vulnerability associated with each finding,vulnerabilities detection system 100 may assign a risk rating from 1 to10, or as a percentage, or use some other suitable rating system.Security report 118 may also contain one or more recommendations on howto address the security finding, or provide a ‘fix’ for the problem.Such recommendations and risk assignments may be based on aknowledgebase (not shown) derived from subject matter expertise indetecting and correcting such software vulnerabilities.

The methods of the invention describe the steps required to operatesoftware vulnerabilities detection system 100 of FIG. 1. In thepreferred embodiment, computer program 102 is executed at least once andthe flow of unsafe data through the program is first recorded in a dataflow file 140 as shown in FIG. 4. Based on the contents of data flowfile 140, data flow model 114 is populated. The format of data flow file140 can be any suitable file format, such as XML, plain text, any othermarkup format, or a binary (or compiled) format, without departing fromthe principles of the invention.

In the preferred embodiment, three lists, Unsafe1, Unsafe2, Unsafe3 arecreated for each instruction. Persons with average skill in the art willunderstand that these lists can be linked lists, arrays or any otherappropriate data structures of computer software without departing fromthe principles of the invention. Compiled code 104 is scanned to findeach instruction where an external input is supplied to the program,denoting unknown, unsafe or ‘taint’ data. If that instruction calls anunsafe function on the unsafe data, that instruction is added to anotherlist, Worklist. Persons skilled in the art will again understand thatWorklist can be a linked list, an array or any other suitable datastructure. List Worklist 160, Unsafe1 list 180, Unsafe2 list 184 andUnsafe3 list 186 are shown in FIG. 5 along with the other elements ofthe invention as taught earlier.

Next, a set of concurrent worker threads are spawned, each threadselecting and processing an instruction at random from Worklist 160 ofFIG. 5. Based on instruction model 110, control flow graph 112 and dataflow model 114, for each instruction in Worklist 160, Unsafe1 list 180is populated with incoming unsafe data at that instruction, Unsafe2 list182 with unsafe data currently being processed by that instruction, andUnsafe3 list 184 with unsafe data that has been fully processed by thatinstruction. As the worker threads process the instructions of compiledcode 104, the contents of Unsafe1 list 180, Unsafe2 list 182, Unsafe3list 184 for each instruction are updated based on control flow graph112 of that instruction as data flows from its Unsafe1 list 180 toUnsafe2 list 182 to Unsafe3 list 184 and into Unsafe1 list 180 of thesuccessor instruction.

If new unsafe data is added to Unsafe1 list 180 of an instruction thatcalls an unsafe function, a new security finding 200 is created andadded to security report 118 as represented in FIG. 5, and thatinstruction is re-added to Worklist 160, and the above process isrepeated. Ultimately, the spawning of worker threads is concluded whenthere are no more unsafe instructions left in Worklist 160, or apredetermined timeout period has elapsed during the above processing.FIG. 6 shows the above algorithm in a flowchart format where an unsafeinstruction denotes an instruction that calls an unsafe function onunsafe data as explained above, and the label instr is used toabbreviate the term instruction.

Referring to FIG. 5, concurrency locks 190, 192, 194 are provided foreach of Unsafe1 list 180, Unsafe2 list 182 and Unsafe3 list 184respectively, and at each step of the above processing, these locks areused to ensure the integrity of the contents of these lists. When a listis no longer being used, its concurrency lock is released (unlocked).Those skilled in the art will understand how the contents of Unsafe1list 180, Unsafe2 list 182 and Unsafe3 list 184 will be updated asexplained above.

Further explained, when a worker thread selects an instruction toprocess from Worklist 160, it locks its Unsafe2 list 182 and Unsafe3list 184, and also temporarily locks its Unsafe1 list 180 while itimports data from its Unsafe1 list 180 to Unsafe2 list 182. The workerthread then statically analyzes the currently selected instruction todetermine from its incoming unsafe data in Unsafe1 list, currentlyprocessed data in Unsafe2 list and fully processed data in Unsafe3 list,what other instructions that unsafe data may propagate to. Thisdetermination is based on the attributes of the current instruction ascontained in its instruction model 110, and any other custom unsafe datapropagation rules pre-defined or provided by the user.

Examples of custom unsafe data propagation rules include specifying thata function or method, e.g. execSqlStatement(String query), should neverreceive unsafe or “taint” user input in its first and only parameter.Such a rule could be expressed as an XML file defining regularexpressions to identify the specific class and method for this call,along with a numeric value identifying that the first parameter shouldnever be tainted or uncontrolled, along with security informationdefining the security impact of such a condition. Another example wouldbe a rule which identifies that the subString(Integer from) call willpropagate the value of its object instance to its return value, whichcould be similarly expressed in an xml file, and identifying the returnvalue. Still other examples of custom rules include source rules, whichdefine the insertion of uncontrolled or tainted data into a program andcleanse rules which define methods that are known to control data suchthat the data can afterwards be considered safe in one or more ways.

Referring back to FIG. 5 and preceding teachings, based on control flowgraph 112 of the current instruction, the current worker threadaggregates all possible control flow destinations of the currentinstruction in a list Next_Instructions (not shown). Subsequently, foreach instruction in Next_Instructions list, the current worker threadlocks its Unsafe1 list and adds outgoing processed unsafe data containedin its Unsafe3 list 184, to the incoming unsafe data contained inUnsafe1 list 180 of the instruction selected from Next_Instructionslist. As explained above, if unsafe data is added to Unsafe1 list of aninstruction that calls an unsafe function, a security finding 200 isadded to security report 118 and that instruction is re-added toWorklist 160. The above process continues until there are no moreinstructions left to process in Worklist 160 or a timeout period haselapsed.

In a highly advantageous embodiment, worker threads are distributedacross a multi-core or multi-CPU or multi-machine or multi-nodeprocessing environment to improve the performance of the analysis and toallow processing of very large target software programs. In a similarlyadvantageous embodiment, the traversal of the control flow graph by theworker threads is performed according to custom unsafe data propagationrules provided by the user. In another advantageous embodiment thesecurity findings are created by an analyzer module.

In another advantageous embodiment, security report 118 as shown in FIG.5 contains a full execution trace of unsafe data corresponding to eachsecurity finding 200 populated in security report 118. The executiontrace may contain the origin and termination information for the unsafedata that ultimately caused security finding 200 to be triggered. As anexample, consider that unsafe data was provided as a user input infunction or instruction I1 and it traversed through several interveningfunctions or instructions I2 . . . I9 before being discarded or reset ininstruction I10. Then execution trace for corresponding security finding200 in security report 118 may contain the entire lifecycle or trace ofthat data along with the names/labels of instructions I1 . . . I10 andfilename(s) and corresponding line numbers in the source files fromsource code 106 if available, or obtained from debug information orassembly instructions.

If source code 106 is available, each source file corresponding to theabove trace is parsed into an abstract syntax tree or trees, and theline numbers and offsets for non-keyword identifier tokens is generated.Persons skilled in the art will understand that these non-keywordidentifier tokens will represent user or custom variables, as opposed tokeywords belonging to the grammar of the programming language itself.Using the abstract syntax tree or trees above, corresponding to eachinstruction in the trace, the identifier names and values of anyvariables or processor registers that contained the unsafe data isobtained using the debug information, and then added to the traceinformation.

In addition, security report 118 of FIG. 5 may be properly formatted tobe visually appealing with proper highlighting of important pieces ofinformation for each security finding 200, and contain a human friendlydescription of the finding along with a risk rating or risk factorassigned to the finding by system 100. Depending on the severity of thevulnerability associated with each security finding 200, vulnerabilitiesdetection system 100 may assign a risk rating from 1 to 10, or as apercentage, or use some other suitable rating system.

Security report 118 may also contain one or more recommendations on howto address security finding 200, or ‘fix’ the problem. Suchrecommendations and risk assignments may be based on a knowledgebase(not shown) derived from subject matter expertise in detecting andcorrecting such software vulnerabilities. The knowledgebase may befurther designed to continuously augment its content eitherautomatically or with human assistance or by a combination of bothautomatic and manual means, as vulnerabilities detection system 100operates over time.

In view of the above teaching, a person skilled in the art willrecognize that the apparatus and method of invention can be embodied inmany different ways in addition to those described without departingfrom the principles of the invention. Therefore, the scope of theinvention should be judged in view of the appended claims and theirlegal equivalents.

I claim:
 1. A software vulnerabilities detection system comprising: (a)a non-transitory storage medium storing computer-readable programinstructions; (b) a microprocessor, coupled to said non-transitorystorage medium for executing said program instructions; (c) saidmicroprocessor configured to: (d) receive compiled code; (e) create aninstruction model for each instruction of said compiled code, saidinstruction model comprising instruction location, debug information,instruction type, operands, existing memory state requirements, basicblock membership, function/method membership of each said instruction;(f) create a control flow graph for each said instruction, said controlflow graph comprising all potential control flow paths and abidirectional list of predecessor instructions for each saidinstruction; (g) create a data flow model comprising recorded flow ofunsafe data as observed during the execution of said compiled code; (h)analyze said instruction model, said control flow graph and said dataflow model to create a security finding for each said instruction thatcalls an unsafe function on said unsafe data; and (i) generate asecurity report comprising each said security finding.
 2. The softwarevulnerabilities detection system of claim 1 wherein said compiled codeis instrumented.
 3. The software vulnerabilities detection system ofclaim 1 wherein said instruction model further comprises attributes andplaceholders for attributes, said attributes including values formemory, register information, variable type of each said instruction,pointer aliasing information and unsafe dataflow information.
 4. Thesoftware vulnerabilities detection system of claim 3 wherein saidpointer aliasing information comprises aliasing maps to determine whichpointers may represent the same value given a plurality of control flowsof each said instruction.
 5. The software vulnerabilities detectionsystem of claim 1 further comprising a data flow file for recording flowof unsafe data as it flows during the execution of said compiled code.6. The software vulnerabilities detection system of claim 1 furthercomprising an analyzer module configured to facilitate in at least thecreation of said security finding and the generation of said securityreport.
 7. The software vulnerabilities detection system of claim 1further comprising a set of concurrent worker threads, each said threadprocessing an instruction from said compiled code where an externalinput is supplied.
 8. The software vulnerabilities detection system ofclaim 7 wherein said concurrent worker threads are executed on one ormore selections from the group consisting of a CPU, a processor, a core,a computing machine and a node.
 9. The software vulnerabilitiesdetection system of claim 1 wherein said security report furthercomprises an execution trace of said unsafe data corresponding to eachsaid security finding, said execution trace comprising information fromthe origin to the termination of said unsafe data.
 10. The softwarevulnerabilities detection system of claim 1 wherein said security reportfurther comprises a risk rating, a human-readable description and one ormore remediation recommendations, for each said security finding.
 11. Amethod of detecting software vulnerabilities by a microprocessorexecuting program instructions stored on a computer-readablenon-transitory storage medium, said method comprising the steps of: (a)inputting compiled code; (b) creating an instruction model for each saidinstruction, said instruction model comprising instruction location,debug information, instruction type, operands, existing memory staterequirements, basic block membership, function/method membership andclass membership of each said instruction; (c) creating a control flowgraph associated with each said instruction model, said control flowgraph comprising all potential control flow paths and a bidirectionallist of predecessor instructions for each said instruction; (d) creatingand populating a data flow model; (e) creating a security finding foreach said instruction that calls an unsafe function on unsafe data; and(f) generating a security report comprising information related to eachsaid security finding.
 12. The method of detecting softwarevulnerabilities of claim 11 wherein said instruction model is furtherprovided with attributes and placeholders for attributes, saidattributes including values for memory, register information, variabletype of each said instruction, pointer aliasing information and unsafedataflow information.
 13. The method of detecting softwarevulnerabilities of claim 11 wherein said population of said data flowmodel is performed by an execution run of said compiled code andrecording flow of unsafe data from said execution run.
 14. The method ofdetecting software vulnerabilities of claim 11 wherein said populationof said data flow model is based at least partially on a data flow filein which flow of unsafe data during an execution of said compiled codehas been recorded.
 15. The method of detecting software vulnerabilitiesof claim 11 wherein said compiled code is instrumented.
 16. The methodof detecting software vulnerabilities of claim 11 wherein said securityfinding is created by analyzing said data flow model.
 17. The method ofdetecting software vulnerabilities of claim 11 further comprising thesteps of: (g) creating three lists Unsafe1, Unsafe2, Unsafe3 for eachsaid instruction; (h) scanning said compiled code to determine locationswhere external input is supplied and marking said locations ascontaining unsafe data, and further creating a Worklist of allinstructions at said locations that call an unsafe function; (i)creating a set of concurrent worker threads, each thread selecting aninstruction at random from said Worklist, and processing it according tosaid control flow graph and said data flow model, and populating saidUnsafe1 list with incoming unsafe data at said instruction, Unsafe2 listwith unsafe data currently being processed by said instruction, andUnsafe3 list with unsafe data that has been fully processed by saidinstruction; (j) adding an instruction to said Worklist in step (i)above if said instruction has new data added to its said Unsafe1 listand said instruction further calls an unsafe function, and repeatingstep (i); and (k) concluding said creating of said worker threads if allinstructions in said Worklist have been processed as specified in steps(i) and (j) above.
 18. The method of detecting software vulnerabilitiesof claim 17 wherein said concurrent worker threads are executed on oneor more items selected from the group consisting of a CPU, a processor,a core, a computing machine and a node.
 19. The method of detectingsoftware vulnerabilities of claim 17 further applying concurrency locksto ensure integrity of said data populated in said lists Unsafe1,Unsafe2, Unsafe3, and releasing each said concurrency lock correspondingto each said list Unsafe1, Unsafe2 and Unsafe3, if said list is not inuse.
 20. A method of detecting software vulnerabilities by amicroprocessor executing program instructions stored on acomputer-readable non-transitory storage medium, said method comprisingthe steps of: (a) inputting compiled code and source code that resultedin said compiled code; (b) creating an instruction model for each saidinstruction, said instruction model comprising instruction location,debug information, instruction type, operands, existing memory staterequirements, and basic block membership of each said instruction; (c)creating a control flow graph associated with each said instructionmodel, said control flow graph comprising all potential control flowpaths for each said instruction; (d) creating and populating a data flowmodel comprising recorded flow of unsafe data as observed duringexecution of said compiled code; and (e) creating a security finding foreach said instruction that calls an unsafe function on unsafe data.